In the art of rotary irrigation sprinklers, for example, of the pop-up type disclosed in U.S. Pat. Nos. 4,026,471, 4,773,595, 4,892,252, 4,971,250, 5,174,501 and 5,526,982, it has been found desirable to vary the flow rate of water flowing through the sprinkler and discharged from the nozzle head as it rotates to provide a more uniform radial distribution of water from the nozzle head, regardless of whether the water is discharged in a single stream from a single nozzle orifice or is discharged from multiple orifices in the nozzle head. Uniform radial distribution of water is desirable whether the water is being distributed in a full circular pattern or in a part circular pattern.